Page 2
0
0
.
We5fem EIeciYrric
SYNCHRONIZED FREQUENCY MODULATION
RADIO TRANSMITTING EQUIPMENT
504A- I
- 3000 wfltts
FREQUENCY RANGE:
42 to 50 Megacycles
l
A development of Bell Telephone Laboratories, the Research
Laboratories of the American Telephone and Telegraph
Company and the Western Electric Comnany
Foremost among the problems presented by frequency modulation is that of
stability of the mean frequency. The solution of this problem is found in a new
system,- SYNCBRCNIZED Frequency Modulation - developed by Bell Telephone La.bcra-
tories and incorporated in Western Electric% new Radio Transmitter, the 504A-1.
The use of synchronized frequency modulation has made possible stability of the
mean carrier frequency to better than + 1000 cycles, and compared with the Fed-
eral Communication Commissions requirement of f 2000 cycles.
.The mean frequency in a frequencg,modulated sienal is the total number of
cycles occurring in a second, irrespective of their distribution in
time over
this interval.
In SYN~RCNIZED Frequency Modulation this total number of cycles
is, in effect, counted, ccmpared with the number of cycles generated by a Precise
fixed frequency standard, and the tuning of the variable oscillator adjusted
mechanically to keep the two always at exactly the same value. However, ins.tead
.of counting millions of cycles each second, the procedure has been simplified
tremendouslyby the use of a new technique-frequency division. This uermits re-
ducing the frequency to any desired decree. Actually, a frequency of about 5000
cycles or l/8000 of.the carrier frequency is obtained. This low freq.uency, an
exact~submultinle of the carrier frequency, is then comnared to the
OUtuUt of a
lowfrequency crystals oscillator.
Here again another outstanding development, a5 kc crystal oscillator, makes
it nossible to utilize the.virtues of a quartz crystal in meetinc the stability
3
